A study of the contribution of heme iron axial ligation in determining the redox properties of cytochromes is proposed. The main technique to be employed is the Resonance enhanced Raman vibrational spectroscopic technique, with particular concentration on the low frequency, or metal ligand, vibrational region below about 650 cm-1. The study will focus on comparative studies of structurally analogous c-type cytochromes from several species of organism. Eucaryotic cytochrome c (e.g. horse) and Rhodospirillum rubrum cytochrome c2, as well as cytochromes c2 from other species of photosynthetic bacteria will be studied first. Detailed comparisons of the low frequency region of the Rman spectra will be used to obtain structural information pertaining to the heme iron coordination sphere. Differences between the cytochromes will be related to known differences in midpoint redox potential. Solution pH will be varied, and the resonance Raman spectra followed as a function of pH for each cytochrome. Since pH variation of midpoint potentials have been reported for cytochromes c and c2, the observed differences in Raman spectra as a function of pH will be related to the variation in potential. The research will then be extended to a study of the low frequency Raman spectra of other cytochromes, including cytochrome c', a bacterial c-type cytochrome which exhibits pH variation of redox potential and visible absorption spectra.